The present invention concerns a container made of synthetic material comprising a closed bottom wall and an opening in the upper portion opposite the bottom wall, and more specifically, a thermoplastic bottle made according to a blow molding, stretch blow molding or thermoforming method.
It also concerns a method for making a container of synthetic material comprising a closed bottom wall and an opening in the upper portion opposite the bottom wall, and more specifically, a thermoplastic bottle made by blow molding, stretch blow molding or thermoforming, said container having at least one fold line.
Currently, one of the most crucial problems in industrialized countries is collecting and disposing of waste, especially non-biodegradable waste such as, for example, a large variety of synthetic materials. Packaging material, especially thermoplastic bottles made of material such as polyethylene terephtalate (PET), comprises a large portion of such waste. These bottles and other containers currently used for carbonated or non-carbonated beverages and other liquids and powders, are extremely unyielding spite of their relatively thin walls. They are difficult to break when empty and awkward, if not impossible, to flatten by folding. For this reason, they occupy considerable space in trash cans or other waste receptacles, resulting in enormous inconvenience and high disposal costs.
Thermoplastic containers for liquids, solids or powders at atmospheric pressure which have fold lines indicated by a sunken fold in the wall, sometimes in juxtaposition with two raised ridges which do not alter the thickness of the wall, have already been proposed. Other such containers have walls which are thinner along the fold lines (grooves) to facilitate folding along these lines.
In particular, European Publication No. 0 472 504 A2 describes a foldable container with fold lines made during the molding process which consist of grooves of reduced thickness, which in effect weaken the container in that area. This method does not change the internal structure of the material, but decreases resistance of the container walls considerably.
These existing packaging materials are generally made of polyolefins such as polyethylene and polypropylene and have several practical disadvantages and limitations. First, the containers with grooves have diminished tensile strength compared to the given mass of the entire container. Second, the containers with ridges along the fold lines which are not thinner than the wall are difficult to bend along the lines provided. Third, the reason the two types of containers described above do not lend themselves to easy bending by partially breaking the wall along the fold lines is that the material is highly plastic and the "deformation memory" of thermoplastic materials in this highly plastic state tends to cause the wall to unfold spontaneously. Fourth, the containers described above cannot be made of the highly resistant thermoplastic materials necessary, in particular, for packaging liquids under super-atmospheric pressure, such as, for example, carbonated beverages. Actually, containers made of such materials, PET for example, are even less easily bent and broken than the containers described above due to their high elasticity combined with a certain plastic deformability.